U.S. city-dwellers can breathe easier than they have in years. Satellite maps released this week by NASA show a pervasive drop in nitrogen dioxide, which is emitted by cars, trucks, power plants and other combustion-fired machinery. That’s a boon for people who prefer inhaling air to corrosive industrial exhaust.

This NASA video condenses a decade of NO2 levels into ten seconds. Watch it. You can almost smell the oxygen as the unsightly red splotches shrink.

They don’t disappear, however, leaving more than 140 million Americans still breathing potentially harmful amounts of nitrogen dioxide. Accordingly, Obama’s Environmental Protection Agency has tightened regulations on NO2, one of the original gases targeted by the 1971 Clean Air Act. In April, the Supreme Court upheld an EPA rule meant to cut nitrogen and sulfur pollution that crosses state lines; the move aims prevent 34,000 premature deaths a year.

Some of the most dramatic reductions occurred in the New York area, Ohio River Valley and San Francisco, as seen in the images below.

New York:

Satellite data show that New York City has seen a 32 percent decrease in nitrogen dioxide between the 2005-2007 (left) and 2009-2011 (right) periods.

Ohio Valley:

Close up of nitrogen dioxide in the Ohio River Valley averaged over 2005 (top) and averaged over 2011.

San Francisco:

These images show how nitrogen dioxide in the San Francisco Bay area changed between the 2005-2007 (left) and 2009-2011 (right) periods. Source: NASA Goddard's Scientific Visualization Studio